The teichuronic acid of the cell wall of Micrococcus lysodeikticus is synthesized in vitro by a particulate enzyme fraction which utilizes uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), UDP-N-acetylmannosaminuronic acid (UDP-ManNAcUA) and UDP-glucose. Structural characterization of the intermediates involved in this process is continuing. The carrier lipid has been shown by mass spectral analysis to be an undecaprenol. The in vitro reaction product has been shown to be similar to the teichuronic acid isolated from cell walls by chemical degradation procedures and by comparison of nuclear magnetic resonance spectra..